Okružní 31, 638 00 Brno  
legmet@cmi.cz  
 +420 545 555 414 
 
Executive summary for the EC (not part of this legislation)  
‘Gas flow computers’ may be placed on the market and put into use in the Czech Republic as legally 
controlled measuring instruments  pursuant to Act No 505/1990 on metrology, as amended. Pursuant to 
the Act, legally controlled measuring instruments are instruments, which are included in the list of the 
types of legally controlled measuring instruments (Implementing Decree No  345/2002) and, at the same 
time, intended (by the manufacturer/importer) for measurements of relevance to the protection of public interests in the fields of consumer protection, contractual relations, imposition of sanctions, fees, tariffs and taxes, hea lth protection, environmental protection, occupational safety or the protection of other 
public interests protected by special legislation . This means that their purpose is similar to that used for 
defining legally controlled products – measuring instrumen ts and non- automatic weighing instruments 
– under Directives 2014/31/EU and 2014/32/EU. The requirements of this legislation do not apply to 
measuring instruments not placed on the market in the Czech Republic for the above purposes, defined by Act  No 505/ 1990 on metrology.  
The subject matter of the notified legislation is to lay down metrological and technical requirements for the relevant type of legally controlled measuring instruments. This legislation also lays down the tests 
for the purposes of type a pproval and verification of this type of legally controlled measuring 
instruments.  
 (End of executive summary.)  
1. ------IND-  2019 0490 CZ-  EN- ------ 20191018 --- --- PROJET 
P U B L I C   D E C R E E 
As the authority with substantive and territorial juris diction in the matter of laying down metrological 
and technical requirements for legally controlled measuring instruments and stipulating the testing 
methods for type approval and verification of legally controlled measuring instruments pursuant to 
§ 14(1)  of Act No  505/1990, on metrology, as amended (hereinafter the ‘Metrology Act’), and in 
accordance with the provisions of §  172 et seq. of Act No 500/2004, the Code of Administrative 
Procedure (hereinafter the ‘CAP’), the Czech Metrology Institute (hereina fter the ‘CMI’) commenced 
ex officio proceedings on 4 April  2016 pursuant to §  46 of the CAP, and based on the supporting 
documents, hereby issues the following:  
I. 
G E N E R A L   M E A S U R E  
number: 0111- OOP -C083 -18 
laying down metrological and technical requirements for legally controlled measuring 
instruments and testing methods for the type approval and verification of legally 
controlled measuring instruments:  
‘gas flow computers’  General Measure No  0111- OOP -C083 -18 
2 1 Basic definitions  
For the purposes of this General Measure, the  terms and definitions pursuant to VIM and VIML1 and 
the following shall apply:  
1.1 
flow computer  
an electronic device, which receives and processes output signals from flow meters and value converters 
for other inputs  
1.2 
flow meter  
an instrument for measuring the volumetric or mass flow rate of gas  
1.3 volumetric flow rate 
the volume of gas flowing through the flow meter per unit of time  
1.4 mass flow rate  
the mass of gas flowing through the flow meter per unit of time  
1.5 volume delivered or mass delivered  
the volume or mass of gas that has flowed through the flow meter per unit of time  
1.6 rated operating conditions  
the conditions of use, for which the specified metrological characteristics of the measuring instrument 
lie within the defined limits  
1.7 
reference conditions  
the conditions of use prescribed for functional tests of the measuring instrument or for comparison 
between the results of measurement  
1.8 
base conditions  
the specified conditions to which the measured quantity of gas is converted  
1.9 compression factor Z  
the ratio of the volume of a certain quantity of gas at a specified pressure and temperature and the volume 
of the same quantity of gas under the same conditions calculated from the ideal gas equation state  
                                                      
1  TNI 01 0115 International Metrology Vocabulary –  Basic and General Terms and Associated Terms (VIM)  
and the International Vocabulary of Terms in Legal Metrology (VIML) are part  of the technical harmonisation 
compendium ‘Terminology in Metrology’ publicly available at www.unmz.cz.  General Measure No  0111- OOP -C083 -18 
3 2 Metrological requiremen ts 
The verification of the measuring instruments are subject to the metrological requirements applicable at 
the time they were put into circulation.  
2.1 Rated operating conditions  
2.1.1 Ambient temperature range 
Gas flow computers must be capable of operating (within the limits of the maximum permissible errors) 
at least in the temperature range of (−10 to +40)  °C. 
The ambient temperature range for the gas flow computer must be specified by the manufacturer.  
2.1.2 Ambient humidity range  
The relative ambient humidity range must be specified by the manufacturer.  
2.1.3 Reference conditions  
Ambient temperature must be (20 ± 3)  °C and shall not change by more than  
1 °C during the test.  
Relative ambient humidity must be (60 ± 15)  % and shall not change by more than  
10 % during the test.  
2.2 Measuring pressure transducers range 
If a pressure transducer is connected to the flow computer in order to measure the static pressure of gas 
in the measuring system, its measuring range must be appropriate to the needs of the measurement 
applic ation. An absolute gas pressure transducer must be used for absolute pressures of less than 21  bar. 
For absolute pressures equal to or greater than 21 bar, a pressure transducer may be used, while the 
average value of barometric pressure typical at the measuring system’s installation site must be entered 
into the flow computer.  
2.3 Range of the temperature sensor with a transducer  
If a temperature transducer is connected to the flow computer in order to measure the temperature of gas in the measuring system, i ts measuring range must be appropriate to the needs of the measurement 
application. The minimum gas temperature measuring range is 40  °C. 
2.4 Measuring range  
The measuring range of a flow computer is given by the range of the flow meter used.  
2.5 Maximum permissib le error  
The maximum permissible errors expressed as a percentage of the measured value and related to the 
indicated flow rate or quantity of gas delivered are given in Table  1. 
The maximum permissible errors are set separately for reference conditions and  for the range of the set 
operating conditions.  
Table  1 – Maximum permissible errors  
Indication  Reference  
conditions  Rated 
operating 
conditions  General Measure No  0111- OOP -C083 -18 
4 Indication of measured flow rate or measured quantity of gas 
delivered a) ±0.50 % ±1.00 % 
Indication of calculated flow rate or calculated quantity of gas 
delivered b) ±0.20 % ±0.30 % 
Indication of the quantities measured using analogue signal – 
temperature c) ±0.10 % ±0.20 % 
Indication of quantities measured using analogue signal – pressure 
and other quantities d) ±0.20 % ±0.50 % 
a) The values of input quantities are simulated using measuring instruments or input simulators.  
b) The input values are entered as constants.  
c) Refers to thermodynamic temperature expressed in degrees Kelvin.  
d) Refers to the value measured.  
2.6 Gas flow computer software  
The software used in the flow computer must be identifiable (software version)  
and validated using a validated checking program. 
2.7 Analogue inputs of gas flow computers  
The analogue inputs of gas flow computers must comply with the requirements given in Table  1. 
3 Technical requirements  
3.1 Design requirements  
All essential components of gas flow computers must be designed in a manner which  ensures that the 
measurement accuracy of the connected flow rate sensor is not degraded.  
Flow computers must be capable of withstanding the external environment for which they are intended 
and obtain satisfactory results in the relevant electromagnetic co mpatibility tests. If they are intended 
for use in potentially explosive atmospheres, they shall also be covered by a valid approval for this 
purpose.  
In the case of gas flow computers whose connected elements may be disassembled or replaced, all 
connections and interfaces between the flow computer and these elements must be secured.  
Any interfaces and connections allowing for the connection of additional devices shall not affect the metrological characteristics of the flow computer.  
3.2 Indicating device  
Gas flow computers must be equipped with a display. The display must be readable within an angle of 
15° from the perpendicular to the plane of the window. If the indicating device does not use all digits to 
indicate cumulative values, every unused digit to the  left of the highest significant digit shall indicate 
zero.  
3.2.1 Main indications  
The flow computer must be capable of indicating the following on the indicating device:  
  a)  the calculated gas flow rate at measurement conditions;  
  b)  the calculated gas flow  rate at base conditions;  
  c)  the volume of delivered gas at measurement conditions;  
  d)  the volume of delivered gas at base conditions;  General Measure No  0111- OOP -C083 -18 
5   e)  warning indications and alarms. 
3.2.2 Additional indications  
In addition, the gas flow computer must be capable of indicating or displaying the following parameters, 
either on the indicating device or a permanently attached information plate with indelible markings, or 
an external attached indicating device or a combination of the above:  
  a)  the values of the totalis ers; 
  b)  the method of calculation of the delivered quantity of gas;  
  c)  conversion to units of energy for fuel gases;  
  d)  parameters of the gas flow sensor;  
  e)  parameters of the measured gas (e.g. compression factors, the isentropic exponent, dyn amic 
viscosity, critical gas variables);  
  f)  methods for calculating the parameters of the measured gas;  
  g)  base condition values;  
  h)  the values of the measured quantities (e.g. pressure p and temperature t  at measurement 
conditions);  
  i)  the version of the flow computer software used, including the checksum.  
The identification and units of every quantity or parameter that can be indicated must be clearly 
displayed on or near the flow computer display. 
 
3.3 Warning indications and alarms  
Gas flow c omputers must be capable of detecting:  
• that any of the measured or calculated values are outside the specified ranges,  
• that the instrument is operating outside the limits of validity of the computing algorithm;  
• that any of the electrical signals are outsid e the range of the input of the flow computer;  
• an expiring battery.  
With the exception of the indication of an expiring battery, as long as such a defective operation is 
detected by the flow computer, any further increase of the volume of gas delivered is not permitted. The 
volume of delivered gas may continue to increase only if it is possible to accurately identify the quantity 
that has passed through during the period of defective operation, for example by means of additional 
‘error volume of delivered g as’. 
The resetting of a triggered alarm must only be possible if the cause of the alarm has been eliminated. 
Resetting must be secured against unauthorised access.  
If the flow computer is capable of estimating the quantity of gas passed through the measuring system during the duration of the faulty condition(s), measures must be taken to prevent confusion between 
estimated values and the values measured during the period without a faulty condition or conditions. 
The estimated values must be stored in memory  
and indicated separately.  
After the cause for the interruption, alarm or failure no longer exists and the stored values are restored, the gas flow computer must be capable of restarting automatically.  
It must be impossible to change the parameters used in the processing of measurements or intended to identify the constituent parts of the system, except by a person authorised to make such changes. There 
must be a way of monitoring these parameters. Any change to these parameters must either require seals 
to be broken, or must be recorded by the flow computer together with an identifier specific to the person 
making the change and the date of the change.  General Measure No  0111- OOP -C083 -18 
6 3.4 Flow meter error correction  
The gas flow computer may be equipped with flow meter error correction functions. If this function is 
activated and used, it must be ensured that the flow meter’s error curve is relevant to the actual operating 
conditions at the flow meter’s  site of installation. This means that the flow meter must be verified under 
conditions close to those under which it is used in application at the installation site and preferably using 
the gas used at the installation site, unless the type approval certi ficate allows another method.  
3.5 Input from the flow meter  
The flow computer must have an input that can process the signal from the connected flow meter. It is 
permissible for a single flow computer to process signals from multiple connected flow meters, if its 
design is adapted for this purpose.  
3.6 Methods for the calculation of the compression factor 
Only generally accepted and validated methods may be used for the calculation of gas compression 
factors.  
The compression factors or their ratio or constant value s must be used in the flow computer whenever 
it is clear that the static (absolute) pressure value in the measuring system can reach 4 bar.  
3.7 Software  
Software critical for metrological characteristics of the gas flow computer must be validated, readily 
identifiable and secured. Evidence of any intervention in the software must be available.  
Access to change the software must only be obtainable by using a password or a code that can be updated, or by using a specified device after breaking the official verifi cation mark.  
3.8 Security  
The flow computer must be constructed in such a way that any intervention able to influence the results 
of measurement will cause visible damage to the flow computer or its official marks, or activate an 
alarm, which must be stored in the event register me mory.  
If access to the authorised or approved settings of the flow computer is secured in electronic form, the 
following requirements must be fulfilled:  
  a)  access must only be obtainable by using a password or a code that can be updated or by using a 
specified device;  
  b)  the last intervention must be registered in the flow computer’s memory; at least 100 interventions must be registered, including the date and time of the intervention and specific 
identification of the intervention;   
 
 c)  it must be possible to obtain access to the intervention(s) registered in the memory. It shall not 
be possible to erase or overwrite the memory without breaking the official mark or using the 
security password or code.  
All connections and interfaces between the fl ow computer and the connected elements of the measuring 
system must be secured.   
3.9 Degree of protection provided by enclosure 
The gas flow computer shall, by means of suitable construction, provide sufficient protection against 
contact with dangerous parts, infiltration of foreign particles and water ingress corresponding to the use 
specified by the manufacturer. The degree of protection provided by the enclosure must be indicated.  General Measure No  0111- OOP -C083 -18 
7 3.10   Potentially explosive atmospheres  
Gas flow computers intended for use in p otentially explosive atmospheres shall comply with the 
requirements specified in the relevant regulations.  
3.11   Electromagnetic compatibility  
Gas flow computers shall either not be affected by electrical or electromagnetic interference or shall 
respond to it  in a defined manner (for example by reporting an error, inhibiting measurement, etc.). In 
addition, they may not emit unwanted electromagnetic fields.  
4 Instrument markings  
The markings must be placed so that they are clearly visible and must be permanent u nder normal 
conditions of use of the flow computer.  
4.1 Statutory markings  
At least the following information must be indicated on every gas flow computer:  
  a)  the identification mark or name of the manufacturer;  
  b)  type designation;  
  c)  the year of man ufacture;  
  d)  the serial number;  
  e)  the type approval mark.  
A label with the following information may be affixed to a gas flow computer:  
  f)  the version of the applied computer software;  
  g)  the parameters of the measured gas;  
  h)  the ranges of  the input sensors used.  
4.2 Placement of the official mark  
A suitable place must be provided for affixing the official mark(s). The placement of the marks must be specified in the type approval certificate.  
The access to any elements or communication ports of  the flow computer by means of which the 
measuring system’s metrological parameters may be changed must be appropriately secured.  
5 Type approval of the measuring instrument  
5.1 Overview of the tests  
The process of type approval of a gas flow computer comprises the following tests and activities:  
a) external inspection;  
b) accuracy test under reference conditions;  
c) test of resistance to limit ambient temperatures;  
d) dry heat test;  
e) damp heat test;  
f) test of the effect of supply voltage;  
g) test of the effect of short -time DC power variations;  
h) test of the effect of fast transient/burst disturbances;  General Measure No  0111- OOP -C083 -18 
8 i) test of the effect of surges;  
j) test of the effect of the electromagnetic field;  
k) test of the effect of electrostatic discharge;  
l) test of the effect of conducted disturbances induced by  radio -frequency fields;  
m) test of the effect of power frequency magnetic fields;  
n) test of the effect of short -term AC power variations;  
o) vibration resistance test;  
p) shock resistance test;  
q) stability test;  
r) test of warning functions and error states;  
s) test of the protection provided by enclosure.  
5.2 External inspection  
The following shall be assessed by external inspection of the gas flow computer:  
• the completeness of the required technical documentation;  
• the conformity of the metrological and technical characteristics specified by the manufacturer in 
the documentation with the requirements of this regulation specified in Articles  2 and 3;  
• the completeness and condition of the gas flow computer according to the prescribed technical 
documentation;  
• conformi ty of the version of the measuring instrument’s calculator software with the version 
specified by the manufacturer.  
5.3 Test conditions during type approval  
5.3.1 Requirements for test equipment and validation means  
Measuring instruments used as testing equipment shall have valid metrological traceability. The expanded measurement uncertainty (for k  = 2) of the test equipment must be less than or equal to ¼ of 
the maximum permissible error of the tested measuring instrument or ¼ of the maximum permissible error of th e relevant analogue input. Control programs must have a valid validation certificate for all the 
calculation methods used.  
5.3.2 Test conditions  
Ambient temperature during the test must be within the range of (20 ± 3)  °C. Changes in ambient 
temperature throughout the test may not exceed 1  °C. 
Relative ambient humidity must be within the range of (60 ± 15)  %. Ambient relative humidity may not 
change by more than 10 % during the test.  
These reference conditions must be complied with during accuracy tests of the gas  flow computer.  
5.4 Functional tests  
5.4.1 Accuracy test under reference conditions  
5.4.1.1  Accuracy test of the calculator software  
The data calculated by the gas flow computer shall be checked at least at five points evenly spaced over 
the whole range. If multiple variabl es enter the calculation, various combinations of these variables must 
be checked. For each input, at least three points evenly spaced over the whole range of the given quantity 
shall be chosen. For other quantities, values close to their operating points shall be chosen.  General Measure No  0111- OOP -C083 -18 
9 The error of the value calculated by the flow computer shall not exceed the maximum permissible errors 
given in Table  1. 
5.4.1.2  Test of accuracy of the analogue inputs  
The data on the gas flow computer’s analogue inputs shall be checked at least at five points (including 
points close to the lower and upper limits of the measuring range) evenly spaced over the whole range.  
The error on the flow computer’s analogue inputs may not exceed the maximum permissible errors given 
in Table  1. 
5.4.2 Test of resistance to limit ambient temperatures  
When testing the gas flow computer for resistance to limit temperatures, it shall be subjected to an 
accuracy test at ambient limit temperatures at points specified according to paragraph 5.4.1.  
The ambient temperat ure value shall correspond to the lower and upper ambient temperature limits 
specified in 2.1.1 or by the manufacturer.  
At each test point and each measurement, the error must be within the maximum permissible errors 
specified for operating conditions according to Table  1. 
After the tests, all sub -functions of the measuring instrument must operate correctly. 
5.4.3 Damp heat test  
The gas flow computer shall be exposed to the effect of a constant temperature equal to the upper limit 
temperature of the environmental  class and to a constant relative humidity of 93  % for a period of four 
days. Condensation of water may not occur on the measuring instrument during the test.  
At each phase of the test, the gas flow computer shall be subjected to an accuracy test according  to 
paragraph 5.4.1 at a limited number of points, namely:  
  a)  at reference conditions (before the increase of temperature),  
  b)  at the end of the upper limit temperature phase,  
  c)  at reference conditions (after the decrease of temperature).  
At each  test point and each measurement, before, during and after the test, the error must be within the 
maximum permissible errors for the reference conditions or, if applicable, the specified operating 
conditions, according to Table  1. 
After the tests, all sub -functions of the measuring instrument must operate correctly. 
5.4.4 Damp heat test, cyclic test  
The gas flow computer shall be exposed to cyclic temperature variation between temperature at reference conditions and the upper limit temperature of the environmenta l class. Humidity must be 
maintained above 95 % during the temperature change and the low temperature phases and above 93  % 
during the upper limit temperature phases. Condensation of water may occur on the measuring instrument during the test.  
At each phase of the test, the gas flow computer shall be subjected to an accuracy test according to paragraph 5.4.1 at a single test point chosen inside the specified field of measurement of the gas flow 
computer, namely:  
  a)  at reference conditions (before the cyclic variations),  
  b)  at reference conditions (after the cyclic variations).  
At each test point and each measurement, before and after the test, the error must be within the maximum 
permissible errors specified for reference conditions in Table 1. 
After t he tests, all sub -functions of the measuring instrument must operate correctly. General Measure No  0111- OOP -C083 -18 
10 5.4.5 Test of the effect of supply voltage  
The test consists of exposing the test equipment to the effect of fluctuation of power conditions while 
the test equipment operates.  
When testing gas flow computers for the effect of fluctuations in the magnitude of supply voltage, the 
measuring instrument shall operate as designed and its error must be within the maximum permissible errors given in Table 1.  
a) In the case of gas flow computers powered by an AC power supply with one nominal voltage U
N 
and one nominal frequency f N, the test shall be carried out sequentially for the following pairs of 
set points: [ pmin, Tmin]; [p max, Tmin]; [p max, Tmax]; [p min, Tmax] at power conditions sequential ly set to:  
Order Frequency  Voltage  
1 fN 1.10U N 
2 fN 0.85U N 
3 1.02 f N UN 
4 0.98 f N UN 
b) In the case of gas flow computers powered by AC power mains with a range of nominal voltages 
from UN1 to UN2 and one nominal frequency fN, the test shall be carried out sequentially for the 
following pairs of set points: [ pmin, Tmin]; [p max, Tmin]; [p max, Tmax]; [p min, Tmax] at power conditions 
sequentially set to:  
Order Frequency  Voltage  
1 fN 1.10U N 
2 fN 0.85U N 
3 1.02 f N UN 
4 0.98 f N UN 
c) In the case of gas flow computers powered by external DC voltage with a range from U N1 to UN2, 
the test shall be carried out sequentially for the following pairs of set points: [ pmin, Tmin];  
[pmax, Tmin]; [p max, Tmax]; [p min, Tmax] at power conditions sequentially set to UN1 and UN2. 
Before the error is established, the supply voltage must be stabilised at the set value.  
d) In the case of gas flow computers powered by external batteries, the test shall be carried out sequentially for the following pairs of set points: [ p
min, Tmin]; [p max, Tmin]; [p max, Tmax]; [p min, Tmax] 
at power conditions sequentially set to U min and Umax, where Umin and Umax are values of voltage 
specified by the manufacturer of the test equipment.  
Before the error is established, the su pply voltage must be stabilised at the set value.  
5.4.6 Test of the effect of short -time DC power variations  
The test consists of exposing the test equipment to the effects of short -term DC power variations while 
the test equipment operates.  
Before the applicati on of the disturbance, the error on volume at a single point chosen inside the 
specified field of measurement of the gas flow computer must be established. The error before the 
application of the disturbance must be within the maximum permissible errors at  reference conditions 
given in Table  1. 
The test shall be carried out sequentially for the following dips and short interruptions:  General Measure No  0111- OOP -C083 -18 
11 Order Residual voltage  Duration  
1 0 % U T ½T 
2 0 % U T 1T 
3 70 % U T 25T 
4 0 % U T 250T  
where U T is the equipment’s rate voltage and T is the power frequency period.  
UT shall be determined as follows:  
a) If a single rated supply voltage is specified for the test equipment, this value shall be used.  
b) If a range of rated voltages is specified for the test equipment and this range does not exceed  
20 % of the lower value of the supply voltage range, then any single voltage from the specified 
range shall be used as the rated supply voltage.  
c) If a range of rated voltages is specified for the test equipment and this range exceeds  
20 % of the lower value of the supply voltage range, then the test procedure must be repeated for both the lower and the upper voltage limits specified.  
For each combination of test  voltage and period of duration, 3 disturbances shall be applied at an interval 
of 10 seconds or longer. Each series of failures must begin gradually at phase angles of 0°, 90°, 180° 
and 270°, except for the failure with a duration of 250 T, where the test may only be conducted at 0°. 
When testing the effect of variations in the magnitude of supply voltage, in the case of gas flow 
computers, the measuring instrument shall operate as designed and the difference between the errors 
recorded before and during the application of the disturbance may not exceed the maximum permissible 
errors at reference conditions given in Table 1, with the exception of disturbances with a duration of 
250T , in which the activation of the test equipment’s safety and warning devices in accordance with 
Article  3.3 of this regulation is considered to be an acceptable response to the disturbance applied.  
5.4.7 Test of the effect of fast transient/burst disturbances 
The test consists of exposing the test equipment to the effect of fast transie nt/burst disturbances while 
the test equipment is operating.  
Before the application of the disturbance, the error on volume at a single point chosen inside the 
specified field of measurement of the gas flow computer must be established. The error before th e 
application of the disturbance must be within the maximum permissible errors at reference conditions given in Table  1. 
The gas flow computer’s resistance to fast transient/burst disturbances shall be tested using burst pulses 
of ±2 kV on the terminals fo r connecting AC or DC mains power and ±1  kV on the terminals for 
connecting AC mains power that are not connected to DC mains power and on signal, communication and control lines longer than 3 metres. The pulse repetition frequency shall be 5 kHz, the burs t 
disturbance repetition interval shall be 300 ms and the total duration of the test for each of the inputs 
and one pulse polarity shall be at least 1 minute.  
When testing the effect of fast transient/burst disturbances, in the case of gas flow computers, the measuring instrument shall operate as designed and the difference between the errors recorded before and during the application of the disturbance may not exceed the maximum permissible errors at 
reference conditions given in Table  1. 
5.4.8 Test of the effec t of surges  
The test consists of exposing the test equipment to the effect of a surge while the test equipment operates.  General Measure No  0111- OOP -C083 -18 
12 Before the application of the disturbance, the error on volume at a single point chosen inside the 
specified field of measurement of the gas flow computer must be established. The error before the 
application of the disturbance must be within the maximum permissible errors at reference conditions 
given in Table  1. 
The gas flow computer’s immunity to surges shall be tested using a surge of  
tr/th = 1.2/50 (8/20)  µs and max. voltage of ±2 kV asymmetrically and ±1  kV symmetrically on AC or 
DC main supply inputs and ±1 kV asymmetrically or ±0.5  kV symmetrically on signa l, communication 
and control lines longer than 30 m or lines placed (even partially) outside buildings regardless of their length. For each polarity and each test voltage level, 3 pulses shall be applied. The pulse repetition 
period shall be 1 minute or longer. 
When testing the effect of surges, in the case of gas flow computers, the measuring instrument shall 
operate as designed and the difference between the errors recorded before and during the application of 
the disturbance shall not exceed the maximum permissible errors at reference conditions given in 
Table  1. 
5.4.9 Test of the effect of electromagnetic fields  
The test consists of exposing the test equipment to the effects of electromagnetic fields while the test 
equipment operates.  
Before the application of  the disturbance, the error on volume at a single point chosen inside the 
specified field of measurement of the gas flow computer must be established. The error before the 
application of the disturbance must be within the maximum permissible errors at reference conditions 
given in Table  1. 
The test shall be conducted in the frequency range of 80 MHz to 2,000 MHz in an electromagnetic field 
with a strength of 10 V/m (the value of the unmodulated carrier). The carrier is amplitude modulated at 
a depth of 80 %, the modulation signal being a sine wave at a frequency of 1  kHz. The frequency step 
of the test field wobble shall not be more than 1 %; the delay period for each frequency shall not be less 
than the time needed to examine the test equipment or for the t est equipment to respond to the 
disturbance; it may not be shorter than 0.5 seconds in any case. The test field is applied to all sides of the enclosure of the test equipment.  
When testing the effect of electromagnetic fields, in the case of gas flow compu ters, the measuring 
instrument shall operate as designed and the difference between the errors recorded before and during 
the application of the disturbance may not exceed the maximum permissible errors at reference 
conditions given in Table  1. 
5.4.10  Test of the  effect of electrostatic discharge 
The test consists of exposing the test equipment to the effects of electrostatic discharges while the test 
equipment operates.  
Before the application of the disturbance, the error on volume at a single point chosen inside  the 
specified field of measurement of the gas flow computer must be established. The error before the 
application of the disturbance must be within the maximum permissible errors at reference conditions 
given in Table  1. 
The test shall be carried out using a contact discharge of 8  kV or an air discharge of 15 kV. 
The discharges shall be applied to the enclosure of the test equipment and the coupling plane adjacent 
to the test equipment.  
When testing the effect of electrostatic discharge, in the case of gas flow computers, the measuring 
instrument shall operate as designed and the difference between the errors recorded before and during the application of the disturbance shall not exceed the maximum permissible errors at reference 
conditions given in Table  1. General Measure No  0111- OOP -C083 -18 
13 5.4.11  Test of the effect of conducted disturbances induced by radio -frequency fields  
The test consists of exposing the test equipment to the effects of conducted disturbances induced by 
radio -frequency fields while the test equipment operates.  
Before the appli cation of the disturbance, the error on volume at a single point chosen inside the 
specified field of measurement of the gas flow computer must be established. The error before the application of the disturbance must be within the maximum permissible error s at reference conditions 
given in Table  1. 
The test shall be conducted in the frequency range of 0.15 MHz to 80  MHz at an open circuit voltage of 
10 V (the value of the unmodulated carrier). The carrier is amplitude modulated at a depth of 80 %, the 
modul ation signal being a sine wave at a frequency of 1  kHz. The frequency step of the test field wobble 
shall not be more than 1 %; the delay period for each frequency shall not be less than the time needed 
to examine the test equipment or for the test equipme nt to respond to the disturbance; it may not be 
shorter than 0.5 seconds in any case. The disturbances shall be applied to signal lines longer than 
3 metres, all DC mains inputs and outputs and all AC mains inputs and outputs, as well as functional earth connections.  
When testing the effect of conducted disturbances induced by radio- frequency fields,  
in the case of gas flow computers, the measuring instrument shall operate as designed and the difference between the errors recorded before and during the application of the disturbance may not exceed the 
maximum permissible errors at reference conditions given in Table 1.  
5.4.12  Test of the effect of power frequency magnetic fields 
The test consists of exposing the test equipment to the effects of the magnetic field while the test equipment operates.  
Before the application of the disturbance, the error on volume at a single point chosen inside the 
specified field of measurement of the gas flow computer must be established. The error before the 
application of the disturbance  
must be within the maximum permissible errors at reference conditions given in Table 1. 
The test shall be conducted at a frequency of 50 Hz or 60 Hz in a magnetic field with a strength of 
100 A/m for a permanently acting field and 1,000 A/m for a s hort-acting field (exposure time 1  s to 3 s). 
The test field shall be applied to all sides of the enclosure of the test equipment using a coil positioned 
so that the test equipment is in the centre of the coil (immersion method).  
When testing the effect of  electromagnetic fields, in the case of gas flow computers, the measuring 
instrument shall operate as designed and the difference between the errors recorded before and during the application of the disturbance may not exceed the maximum permissible errors  at reference 
conditions given in Table  1. 
5.4.13  Test of the effect of short -time AC power variations  
The test consists of exposing the test equipment to the effects of short -term AC power variations while 
the test equipment is operating.  
The test only applies t o low voltage DC power supplied to the ports from external DC supply mains. It 
does not apply to flow computers powered by, for example, an internal battery. 
Before the application of the disturbance, the error on volume at a single point chosen inside the  
specified field of measurement of the gas flow computer must be established. The error before the 
application of the disturbance  
must be within the maximum permissible errors at reference conditions given in Table 1. 
The test shall be carried out sequent ially for the following dips and short interruptions:  
Order Residual voltage  Duration  
1 0 % U  10 ms  General Measure No  0111- OOP -C083 -18 
14 2 0 % U  30 ms  
3 70 % U  300 ms  
4 0 % U  1,000 ms  
where U  is the rated voltage of the device.  
The steps of the test at a residual voltage of 0  % U must be conducted when simulating both a 
disconnection of power supply (high impedance state) and a line short -circuit (low impedance state).  
U shall be determined as follows:  
a) If a single rated supply voltage is specified for the test equipment, this valu e must be used.  
b) If a range of rated voltages is specified for the test equipment and this range does not exceed  
20 % of the lower value of the supply voltage range, then any single voltage from the specified 
range shall be used as the rated supply voltage. 
c) If a range of rated voltages is specified for the test equipment and this range exceeds  
20 % of the lower value of the supply voltage range, then the test procedure must be repeated for both the lower and the upper voltage limits specified.  
For each com bination of test voltage and period of duration, three disturbances shall be applied at an 
interval of 10 seconds or longer.  
When testing the effect of variations in the magnitude of supply voltage, in the case of gas flow 
computers, the measuring instrume nt must operate as designed and the difference between the errors 
recorded before and during the application of the disturbance may not exceed the maximum permissible errors at reference conditions given in Table 1,  
with the exception of disturbances with a duration of 1 second, in which the activation of the test 
equipment’s safety and warning devices in accordance with Article 3.3 of this regulation is considered 
to be an acceptable response to the disturbance applied.  
5.4.14  Vibration resistance test  
During the test of resistance to vibration, before and after being exposed to effects of vibrations, the gas 
flow computer shall be subjected to the accuracy test at reference conditions according to paragraph 
5.4.1 at a limited number of points. While exposed to v ibrations, the gas flow computer does not operate.  
At each test point and each measurement, the error before and after the test must be within the maximum 
permissible errors specified for the reference conditions.  
After the test of resistance to vibrations  has been conducted, all sub- functions of the measuring 
instrument shall operate correctly.  
5.4.15  Shock resistance test  
During the test of resistance to shocks, before and after being exposed to effects of shocks, the gas flow 
computer shall be subjected to the accuracy test at reference conditions according to paragraph 5.4.1 at 
a single test point chosen inside the specified field of measurement of the gas flow computer.  
At each test point and each measurement, the error before and after the test must be within  the maximum 
permissible errors specified for the reference conditions.  
After the test of resistance to shocks has been conducted, all sub -functions of the measuring instrument 
must operate correctly. 
5.4.16  Stability test  
During the stability test, the gas flow computer shall be exposed to:  
• the test of accuracy at reference conditions according to paragraph  5.4.1;  General Measure No  0111- OOP -C083 -18 
15 • the effect of 2 cyclic changes in ambient temperature between the minimum and maximum 
temperatures of the environmental class.  
A cyclic ambient temperature change consists of exposing the measuring instrument to the maximum ambient temperature of the environmental class for 1  week and then exposing the measuring instrument 
to the minimum ambient temperature of the environmental class for 1  week. The chan ges between the 
maximum and minimum temperatures must be made in steps of 10 K·h
-1. 
After stabilisation at reference conditions for a period of 24 hours, the accuracy test at reference 
conditions according to paragraph 5.4.1 must be conducted again.  
At each test point and each measurement, the absolute value of the difference between the error before 
and after the stability test may not exceed ½ of the maximum permissible error at reference conditions 
given in Table  1. 
After the stability test has been cond ucted, all sub -functions of the measuring instrument must operate 
correctly.  
5.4.17  Test of warning functions and error states  
The test shall be conducted by simulating the relevant atypical state. It consists of achieving a set of 
points (simulated states) by in creasing and decreasing the chosen parameter in order to verify that 
warning or error messages are triggered and that the gas flow computer continues to operate correctly 
and records the quantity of gas delivered under these states.  
The warning or error me ssages must be fully identifiable. The flow computer shall record the cause, 
date, start hour and end hour of the warning message and must be capable of recording these messages 
in an appropriate manner. The alarm indications shall remain active until the intervention by an 
authorised person.  
5.4.18  Test of the protection provided by enclosure  
The degree of protection by enclosure of a gas flow computer designed for outdoor use which is not 
intended for installation in a weather -proof cabinet must be at least IP  65. 
During the tests of protection by enclosure, the gas flow computer does not operate. 
After the tests of protection by enclosure have been conducted, all sub- functions of the measuring 
instrument shall operate correctly.  
6 Initial verification  
The initial verification of gas flow computers shall consist of the following tests:  
a) visual inspection;  
b) accuracy test;  
c) test of compatibility of the gas flow computer with the measuring system. 
6.1 Visual inspection  
The purpose of the visual inspection is to check that:  
• the measuring instrument submitted for verification conforms to the approved type;  
• the measuring instrument is not mechanically damaged;  
• the content and implementation of markings and inscriptions correspond to the information and 
requirements specified in  the type approval certificate for the measuring instrument.  
If the measuring instrument fails to meet the visual inspection requirements, no further tests will be 
performed. General Measure No  0111- OOP -C083 -18 
16 6.2 Test conditions during verification  
6.2.1 Test equipment  
The equipment referred to in A rticle  5.3.1 must be used for the test of metrological characteristics.  
6.2.2 Test conditions  
The tests shall be subject to the requirements under Article 5.3.2.  
6.3 Accuracy tests  
6.3.1 Accuracy test of the calculator software  
The calculation software must be tested usin g validated programs for the relevant calculation methods.  
The data calculated by the gas flow computer shall be checked at least at three points evenly spaced over 
the whole range. If multiple variables enter the calculation, various combinations of these  variables must 
be checked. For each input, at least three points evenly spaced over the whole range of the given quantity 
shall be chosen. For other quantities, values close to their operating points shall be chosen.  
The error of the value calculated by the flow computer shall not exceed the maximum permissible errors given in Table  1. 
6.3.2 Test of accuracy of the analogue inputs  
The tests of the analogue inputs must be conducted using reference measuring instruments with 
uncertainties not exceeding ¼ the maxi mum permissible errors of the relevant analogue inputs.  
The data on the gas flow computer’s analogue inputs shall be checked at least at five points (including 
points close to the lower and upper limits of the measuring range) evenly spaced throughout the whole 
range.  
The error on the flow computer’s analogue inputs may not exceed the maximum permissible errors given in Table  1. 
6.3.3 Test of compatibility of the gas flow computer with the measuring system  
The test of compatibility of the gas flow computer with t he measuring system shall be performed at the 
installation site of the system for measuring the delivered quantity of gas.  
The test shall demonstrate compatibility between the gas flow computer and other elements of the 
system for measuring the delivered q uantity of gas. 
Before the flow computer is put into use, the metrological parameter settings must be checked in the 
flow computer’s calculator software, including a check that the parameters are set correctly in relation 
to the actual design of the measur ing system.  
Based on the elements of the measuring system identified at the site of installation and their metrological 
parameters, the overall uncertainty of the measurement of gas flow by the measuring system or the 
accuracy class of the system for measu ring the gas flow rate must be determined.  
For applications where the Q
min parameter has yet to be determined, this parameter must be determined 
as part of the test of compatibility with the elements of the measuring system used and the level of 
compliance  with the installation requirements.  
The Qmin parameter must be entered in the flow computer by means of the flow rate value or the 
corresponding differential pressure value. Then the measuring system may not be permanently operated below this minimum flow  rate.  General Measure No  0111- OOP -C083 -18 
17 7 Subsequent verification  
The subsequent verification procedure is identical to that for initial verification under Chapter  6 except 
for the test of compatibility of the gas flow computer with the measuring system (chapter 6.3.3), which 
is not conduct ed during subsequent verification.  
8   Measuring instrument examination  
When examining measuring instruments pursuant to § 11a of the Metrology Act at the request of a person who may be affected by incorrect measurement, the procedure under Chapter  7 shall  be followed. 
The maximum permissible errors used shall be the maximum permissible errors set for operating 
conditions pursuant to Table  1. 
9   Notified standards  
For the purposes of specifying metrological and technical requirements for measuring instruments and 
specifying the testing methods for their type approval and verification arising from this General 
Measure, the CMI shall notify Czech technical standards, other technical standards or technical 
documents of international or foreign organisations, or other technical documents containing more 
detailed technical requirements (hereinafter ‘notified standards’). The CMI shall publish a list of these 
notified stan dards attached to the relevant measures, together with the General Measure, in a manner 
accessible to the public (at www.cmi.cz ). 
Compliance with notified standards or parts thereof shall be considered, to the extent a nd under the 
conditions laid down in this General Measure, as compliance with those requirements laid down in this 
measure to which these standards or parts thereof apply.  
Compliance with notified standards is one way of demonstrating compliance with the r equirements.  
These requirements may also be satisfied using another technical solution guaranteeing the same or 
higher level of protection of legitimate interests.  
II. 
G R O U N D S 
The CMI issues this General Measure laying down metrological and technical requirements for legally controlled measuring instruments and tests for type approval, verification and examination of legally 
controlled measuring instruments – ‘gas flow computers ’ – in accordance with §  14(1)(j) of the 
Metrology Act to implement § 6(2), § 9(1) and (9), and § 11a(3) of the Metrology Act.  
Under item 1.3.11(j) in the Annex ‘List of the Types of Legally Controlled Measuring Instruments’ to 
Implementing Decree No  345/2002 specifying the measuring instruments whose verification is 
mandatory and measuring instruments subject to type approval, as amended, this type of measuring instruments is classified as instruments subject to mandatory verification.  
This legislation ( General Measure) was notified in accordance with Directive (EU) 2015/1535 of the 
European Parliament and of the Council of 9 September  2015 laying down a procedure for the provision 
of information in the field of technical regulations and of rules on Infor mation Society services.  
III. 
I N S T R U C T I O N S  
In accordance with § 173(2) CAP, no appeals may be made regarding general measures.  General Measure No  0111- OOP -C083 -18 
18 In accordance with the provisions of §  172(5) CAP, decisions on objections are final, and appeals may 
not be made agai nst them. 
Compliance of general measures with legislation may be subject to a review process in accordance with 
§§ 94 to 96 CAP. A party to the proceedings may initiate review proceedings to be conducted by the 
administrative authority which issued this Ge neral Measure. If the administrative authority finds no 
reason to commence the review proceedings, it shall communicate and provide grounds for this fact 
within 30  days. Pursuant to §  174(2) CAP, a ruling on the commencement of review proceedings may 
be issued within three years of the entry into force of the general measure.  
IV. 
E N T R Y   I N T O    F O R C E  
This General Measure shall enter into force on the fifteenth day following the date of posting it on the 
official notice board (§  24d of the Metrology Act).  
 
 
  
 Czech Metrology Institute  
 Director General  
 
 
Posted on:   
Removed on:   
Entry into force: